Interhemispheric communication after section of the forebrain commissures

Cognitive information is shown to be transmitted interhemispherically through channels other than the neocortical commissures, presumably through subcortical pathways. What crosses through these subcortical channels does not appear to include the name or identity of stimuli but rather is more contextual or associative in nature. Results obtained with a technique for prolonged visual lateralization indicate that this information, when used in conjunction with cognitive strategies, allows the cortically disconnected left hemisphere under certain conditions to verbally identify stimuli projected to the right hemisphere or to cross-compare bilateral input. The presence of this subcortical communication would thus appear to help explain some of the increasing exceptions to characteristic disconnection symptoms reported among split-brain subjects. In particular, the present results challenge reports which have attributed oral naming of stimuli in the left visual hemifield to the typical disconnected right hemisphere.

[Developmental changes of the interhemispheric interaction in the tactile function]

This experiment examined the development of the hemispheric specialization and interaction of tactile recognition by the comparison of performance levels in three age groups, i.e. 24 children, 21 adults, and 15 aged people, with the mean ages of 5 yr 7 mo, 22 yr 5 mo and 72 yr 5 mo, respectively. They consisted of right handed males and females in similar numbers, and manifested no abnormality. Stimuli employed were seven random figures approximately 4 X 4 X 0.3 cm in size and placed 30 cm apart at the front of the subjects. Results of the successive interhemispheric matching task revealed that the adults showed the highest and the children showed the worst performance levels among the three groups and the superiority of the left-handed-first condition to the right-hand-first condition was shown in the children whereas no such difference due to hand orders appeared in either the adults or the aged groups. Based on these results, the development on the interhemispheric interaction and hemispheric specialization was discussed.

Cerebral functional asymmetry and MBD children: a synergistic deficit of hemispheres?

The functional cerebral organization of minimal brain-damaged (MBD) children was studied by testing tactile-visual matching of concrete objects. The results revealed that left hand performance was significantly better than the right in the MBD children while normal controls showed no hand difference, and overall performance level was poor for MBD children. These findings are consistent with the view that tactile matching of concrete objects requires hemispheric synergy and that MBD children lack this synergy.

Two brains, one child: interhemispheric information transfer deficits and confabulatory responding in children aged 4, 7, 10

In an investigation of developmental trends in the ability to transfer information between the cerebral hemispheres, 138 children, ages 4, 7, and 10, viewed pictures presented to either the right or left hemisphere and were asked to describe what was viewed. Responses were socored for the number of accurate pictorial features reported (inclusion score), confabulation (erroneous embellishment), perceptual, semantic, and syntactic errors. Misses (failure to provide a response) were also noted. A preponderance of errors were found, such that 4-year olds engaged in a significant degree of confabulatory responding following right vs. left presentation. A significant inverse relationship was found between inclusion and confabulation such that the larger the gap in information reported the greater was the tendency to insert (confabulate) erroneous material. In addition, all children were given a tactile-shape recognition task employing both transfer and non-transfer conditions and requiring tactile exploration and visual recognition. Significantly more errors were found on the transfer vs. non transfer task among the 4-year olds only. In that deficits in information transfer were not complete but only partial, and given that significant intra-hemispheric (non-transfer) errors were also discovered, it was concluded that the hemispheres of children age 4 are not completely but only partially disconnected, and that intra-hemispheric (cortical) immaturity plays a significant role in the production of processing deficits.

Specific spatial defect in a child with septo-optic dysplasia

A blind girl with septo-optic dysplasia was compared with a blind, age-matched control on three spatial tests. Previous observations had suggested a specific spatial learning disorder. Results of the tests showed good verbal intelligence but severe impairment of topographical orientation, route-learning and kinaesthetic memory. It is argued that these dysfunctions were a direct consequence of the malformation syndrome, and could not be accounted for by factors such as sex or congenital blindness.

[Functional hemisphere differences in auditory and tactile recognition in aged people]

The effects of aging on hemispheric specialization in verbal and visuo-spatial functions were examined by dichotic listening and tactile recognition tests. In the first experiment, thirty aged (65-91 year) intact subjects and university students were tested by a dichotic listening tape with pairs of two-syllable meaningful words. The results revealed an overall decline of scores in the aged subjects but there was no interaction between subject and the degree of right ear advantage. In the second experiment, subjects were asked to judged whether successively presented nonsense tactile stimuli to each hand were identical or not. Reaction times and accuracy rates of each hand of the aged subjects were inferior to those of the control subjects. However, no interaction was found between hand and subject group. Both experiments show that there is no evidence to suggest any selective deterioration or specialization of hemispheric function in the aged people, though overall performance level declines with age, which may be caused by short-term memory deficit.

Neuropsychological demonstration of splenial interhemispheric disconnection in a case of "optic anomia"

A patient is described whose neuropsychological deficit corresponded to the notion of "optic aphasia" or, better, optic anomia. The functional deficit was undirectional, i.e. there was a severe impairment in the naming of visually presented stimuli without impairment in the comprehension of the corresponding names. The splenial disconnection was demonstrated by intact cross modal matching within the right hemisphere as well as preserved left-handed tactile naming, which is processed via mid-callosal pathways. The psychological interpretation is discussed in terms of visual and tactile semantics, considering also the presumably diffuse cerebral organization of semantic fields.

Intermanual information transfer in patients with lesions in the trunk of the corpus callosum

Interhemispheric transfer of haptic information was examined in six partially callosotomized patients and three control subjects. Three different portions of the trunk were severed in different subjects. The most anterior 10 mm of the trunk, anterior to the foramen of Monro, was sectioned in one patient. Three other patients had lesions restricted to the anterior part of the trunk posterior to the foramen of Monro. The posterior third of the trunk was damaged in two patients. The splenium, genu and rostrum of the corpus callosum were intact in all six patients, as were the anterior and hippocampal commissures. Poor transfer of haptic information was found only in the three patients with the lesion located in the anterior part of the trunk posterior to the foramen of Monro. The functional anatomy of this region is discussed. It is assumed to house fibers responsible for interhemispheric transfer of complex tactile information.

Wandering and parietal signs in senile dementia of Alzheimer's type

Among a population of nursing home patients with a diagnosis of senile dementia of Alzheimer's type (SDAT), a subgroup was identified who often became lost and wandered even in familiar surroundings. This subgroup differed from the rest of the SDAT patients on tests of parietal function but not on a generalized test of mental status. Thus, wandering in SDAT patients may be an indication of a specific parietal lobe involvement.

Elaboration of representations in a left-handed subject with callosal damage

Four experiments were carried out in a familial left-handed patient who, following a vascular accident, underwent a callosal lesion and had a right hemianopia. Previous observations by Poncet et al. (1978) demonstrated that both hemispheres controlled expressive language. In the first experiment haptic unimanual exploration showed that each system (right hand/left hemisphere; left hand/right hemisphere) elaborated very different mental representations of the stimulus and gave different types of verbal report of it (naming and talking about). In the second experiment, manual exploration of a maze in the search of a target was performed randomly with the right hand and following a competent spatial strategy with the left hand. The third experiment investigated the ability of the right hemisphere to discriminate the phonetic features of the names of objects that were identified but not named. In the fourth experiment, recognition memory of objects was shown to be better when information was processed by the left hand - right hemisphere system than by the right hand - left hemisphere system. Findings are discussed in terms of verbal vs. non-verbal processes and of perceptual awareness.

Proprioceptive contributions to tactile identification of figures: dependence on figure size

Studies on the recognition of objects or shapes explored by a hand or finger have concentrated on the relative merits of different methods of exploration--in particular, whether the exploring hand or finger is moved by the subject himself (active), is guided by an assistant (passive), or remains stationary with the shape being moved by an assistant (tactile). These factors, together with another variable--the size of the explored shape--were investigated in twelve normal adults whose task, without the aid of vision, was to explore and identify various shapes with the tip of the extended right index finger. Two series of shapes were used, a large (15 cm) and small (3 cm) series, both of which consisted of twelve shapes each being a variant of the letter 'S'. The shapes were outlined as rows of Braille-like dots on a flat surface. Exploration was also tested in the proprioceptive mode, in which the exploring hand was guided by an assistant around a shape which was simply drawn on the surface so as to give a minimum of tactile information. For neither large nor small shapes could we demonstrate differences between active, passive and proprioceptive exploration. For the small shapes, the active, passive and proprioceptive modes gave no advantage over purely tactile assessment. However, for the larger shapes, active, passive and proprioceptive modes allowed better identification than movement of the shape. Thus, purely cutaneous signals appear sufficient for optimal discrimination of small figures but proprioceptive signals, generated by movement, are needed for optimal discrimination of larger figures.

Sensibility testing after nerve grafting

This study attempts to establish which sensitivity test is to be preferred for final assessment of recovery of sensibility after nerve grafting. For this purpose seven sensibility tests were performed on patients who had been treated by median nerve transplantation. The findings revealed that the stereognosis test is of greater value for a final evaluation than the two-point discrimination test. This paper discusses several aspects of sensibility tests, e.g. the range of variation of the results and the degree of objectivity.

Preliminary quantitative studies of prehension in squirrel monkeys (Saimiri sciureus)

Squirrel monkeys were filmed in the act of prehending objects of various sizes, shapes, and states of motion. Subsequent three-dimensional analyses indicated that general aspects of prehension do not vary grossly across individuals nor as a function of the object to be prehended, at least at the level of measurement used in these studies. The monkeys exhibited only whole-hand control, even with small or moving objects. However, in comparison with stationary objects, moving objects did elicit variations of arm and hand positions, and were associated with higher frequencies of blinking than nonmoving objects. Some stationary objects also elicited subtle adjustments of movement and form. Sex differences were found in several aspects of prehensive movement and passive joint mobility, but the significance of these findings is not yet clear.

Tactile detection thresholds for a single asperity on an otherwise smooth surface

An investigation was made of the capacities of humans to detect, by actively touching with the fingertip, the presence of a single, small asperity on a very smooth background. The asperity consisted of either a raised dot having a diameter of 602, 231, or 40 micron, or an edge, each etched into a silicon wafer using the methods of contact photolithography. The height of each dot or edge was varied and the subject was asked to make a forced choice on each test trial as to which of two wafers, one of which was blank, contained the asperity. The mean detection threshold, or minimal height of asperity corresponding to a d' of 1.35, was lowest for edges (0.85 +/- 0.22 micron, SD) and increased with decreases in the diameter of dot from 1.09 +/- 0.19 micron for a diameter of 602 micron to 2.94 +/- 1.19 micron and 5.97 +/- 2.02 micron for diameters of 231 micron and 40 micron, respectively. The type of skin displacement required for the detection of these small asperities was believed to be a local lateral deformation of the papillary ridges.

Summation of rapid tactile stimuli in parietal lobe disease

The perception threshold for trains of rapid tactile pulses, applied to the index finger, has been measured in patients with parietal lobe lesions and in patients with median nerve lesions. The former patients had increased perception thresholds for single tactile pulses on the abnormal side. With successively prolonged pulse trains, the threshold decreased exponentially to reach a stable level after 150-400 ms. In contrast, the median nerve patients had increased perception thresholds for tactile pulses irrespective of pulse train duration.

Optic aphasia: a process of interaction between vision and language

A neurological syndrome, called in the literature ether optic aphasia or visual anomia, is defined in principle as the inability to name visually presented objects, together with the preservation of both the ability to identify them by sight correctly and to name them when they are presented in another sensory modality. This syndrome was first described by Freund in 1889, but since then its existence has been continually questioned. When it is accepted, the most common interpretation of it is in terms of an anatomical visuo-verbal disconnection. However, the precise level of the psychological process impaired remains unspecified. The purpose of this paper is threefold. First, evidence is reported showing that a verbal impairment specific to visually presented objects can be observed, as well as analogous syndromes (e.g. tactile aphasia). Secondly, a particular kind of visuo-verbal impairment is defined and called optic aphasia, to distinguish it from other possible cases of visuo-verbal impairments. This syndrome is defined by the specification of the level of the particular psychological process supposed to be impaired, i.e. a disturbance between visual semantics and verbal semantics, both of which operate normally. Thirdly, three hypotheses concerning the operation of the semantic system in normal subjects are derived from the evidence coming from this syndrome.

Cross-modal performance in patients with cerebral lesions

52 patients with circumscribed cerebral lesions, and 35 control patients (lesions in the posterior fossa or in the spinal cord), were assessed for their ability to match spatial configurations: matching was either cross-modal (visual-tactual or tactual-visual). or within-modal (visual-visual or tactual-tactual). They were also tested for cross-modal transfer (visual-tactual or tactual-visual). All materials were "easy" or "hard". Associated defects (e.g. dysphasia, apraxia) were also assessed. It was found that neither site of lesion, nor laterality of lesion, nor presence of any associated defect was significantly and selectively associated with impairment of cross-modal performance.

Agraphesthesia. A disorder of directional cutaneous kinesthesia or a disorientation in cutaneous space

Tests for graphesthesia and for directional cutaneous kinesthesia (DCK) were performed on a large series of neurological patients and normal subjects, in addition to the standard tests for discriminative sensation. Defects in graphesthesia and DCK were found with lesions at all levels of the nervous system. Graphesthesia was more often and more severely affected than DCK. These functions when impaired were always associated with other sensory defects (directional joint kinesthesia, two-point discrimination, etc.) in different combinations. It appears DCK is probably the basis for graphesthesia. Recent experimental studies have provided an anatomic and physiologic basis for DCK and for graphesthesia. These studies have also discredited wide-held beliefs on the transmission of discriminative sensation through the spinal cord. In this light, the history of ideas about sensation and its mediation is reviewed, and it is concluded that DCK alone deserves to be called a "posterior column function". Graphesthesia and DCK are discussed as kinesthetic functions implying orientation in cutaneous sensory space. These are compared to stereognosis and braille reading, which are complex derived functions depending also on motion, but directed towards recognition in external haptic space. Graphesthesia and DCK should both be considered as distinct forms of somatic sensibility which are valuable adjuncts to the clinical sensory examination.

Reeducation of sensation in the hand following nerve suture

In the past decade, sensory reeducation has been widely accepted and applied in patients recovering from nerve injury. The results available for analysis in the few published studies suggest that it is a useful adjunct in patients following nerve repair. The percent of patients achieving the highest level of recovery (S4) and the savings in time (two years instead of five) required to reach this level, are strong testimony to the usefulness of sensory reeducation.